Fuel amount control

ABSTRACT

A method and a device of controlling the amount of fuel delivered to a combustion engine (1), e.g. of two-stroke or four-stroke type, wherein the fuel is supplied through an intake passage (2) intended to deliver air (3) and fuel (4) to the cylinder (5), said intake passage being opened and closed by a piston (6) or by a special valve (7). The fuel supply to the intake passage (2) is effected upstream from the piston (6) or the valve (7) and in response to the opening and closing of the intake passage (2) varying flow speeds and pressures are produced in the passage and the fuel supply system (8) is of a kind the supply amount of which is substantially affected by this variation, such as a carburetor (9) or a low-pressure injection system (10). In order to regulate the fuel supply to the engine fuel a brief cut-off takes place in the fuel-supply system (8) of the entire fuel flow or the part flow and the brief cut-off is arranged to take place to an essential extent during a part of the engine revolution when the intake passage is closed and the fuel supply accordingly is reduced or has ceased.

TECHNICAL FIELD

The subject invention concerns a method and a device to control theamount of fuel delivered to an internal combustion engine to which thefuel is supplied through an intake passage intended to deliver air andfuel to the cylinders. The intake passage is opened and closed by thepiston or by a special valve, and the fuel supply system is of the typethe supply amount of which is substantially affected by said opening andclosing, e.g. a carburettor or a low-pressure injection system.

BACKGROUND OF THE INVENTION

Internal combustion engines of two-stroke or four-stroke type usuallyare equipped with a fuel supply system of carburettor type or injectiontype. In a carburettor, the throttle of the carburettor is affected bythe operator's demand, so that wide open throttle produces a minimumthrottling in the carburettor barrel. The depression created by thepassing air in the carburettor venturi draws fuel into the engine.Traditionally, carburettor engines are equipped with stationary nozzlesor manually adjustable nozzles to regulate the degree ofrichness/leaness of the air-fuel mixture. As the demands on lower fuelconsumption jointly with demands on cleaner exhaust have increased alsoelectronically controlled nozzles have been suggested. In the lattercase the amount of fuel supplied to the carburettor barrel is adjusted.This is effected with the aid of variable throttling. Increasingthrottling gives a leaner air-fuel mixture. The throttling is regulatedcontinuously or in small steps. However, such quantity adjustment iscomparitively complicated and expensive. It is already known to providefor a brief cut-off during the suction phase in order to reduce theamount of fuel or, in accordance with the teachings of DE 23 48 63S, tobriefly open a normally closed valve during the suction phase. It isvery difficult to rapidly open and close a valve, or vice or vice versa,with accuracy. The carburettor is positioned in an intake passageleading to the engine cylinder. This intake passage is opened and closedby the engine piston or by a particular valve, usually called suctionvalve. Owing to this opening and closing of the intake passage varyingflow speeds and pressures generate inside the passage. Since thecarburettor is constructed to allow the depression in the carburettorbarrel to draw in fuel, also the amount of fuel supplied will belargelly affected by the closing and the opening of the intake passage.One consequence of the closing of the intake channel is that the activedepression initially disappears. However, the rapid closure causes anoscillation to be produced in the intake passage, resulting in an activedepression again generating in the carburettor barrel once or severaltimes after closure of the intake passage. Consequently, one or severalfuel feeds occur. Such fuel feeds are not desirable since they do notcorrespond to an actual air flow through the carburettor barrel. Thebasic function of the carburettor is to add an appropriate amount offuel to a predetermined amount of passing air. To a certain extent thisoscillation phenomenon may be considered in the calibration of thecarburettor but since the oscillation is affected by several factors andchanges in response to the engine speed such oscillation results in aless precise fuel supply to the intake passage. This argumentationapplies primarily in the case of carburettor engines wherein the fuelsupply is effected through an intake passage which is opened and closed.But also in fuel injection systems of low-pressure type the injectionedamounts are greatly affected by pressure variations inside the intakepassage.

PURPOSE OF THE INVENTION

The purpose of the subject invention is to considerably lessen theabove-mentioned problems by providing a method and a device to regulatethe amount of fuel supplied to an internal combustion engine equippedwith fuel supply systems of the above type, so as to ensure simple, safeand reliable fuel amount supply.

SUMMARY OF THE INVENTION

The above purpose is achieved by means of a method and a device inaccordance with the invention having the characteristics appearing fromthe appended claims.

Accordingly, the method in accordance with the invention ischaracterized primarily in that in the fuel supply system cut-off iseffected during a part of the operating cycle by means of a shut-offvalve cutting off the entire fuel flow or a part flow, and in that thecut-off is arranged to take place to an essential extent during a partof the operating cycle when the intake passage is closed andconsequently the feed of fuel is reduced or has ceased. Owing to thisshut-off the amounts of fuel supplied in consequence of the aboveoscillation phenomenon in the intake passage may be eliminated which isa definite advantage. In addition, a prolonged cut-off period need onlymoderately affect the amount of fuel supplied. A valve may be moreeasily opened and closed accurately if such actions need not take placevery rapidly. By starting and/or finishing the closure of the shut-offvalve in a precisely defined position with respect to the opening andclosing of the intake passage it becomes possible to precision-regulatethe amount of fuel supplied.

The following description of various embodiments clearly illustrate themanner in which the regulation of amounts is effected and also thevarious particularities and advantages of the invention. The reading issupported by drawing figures and diagrams. The invention is primarilyapplicable in fuel supply systems of carburettor type, as these operateat very low fuel supply pressures. However, the invention is alsoapplicable to fuel injections systems of low-pressure type.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be described in the following in closer details bymeans of various embodiments thereof with reference to the accompanyingdrawings wherein identical numeral references have been used in thevarious drawing figures to denote corresponding components.

FIG. 1 is a schematical illustration of an internal combustion engine oftwo-stroke type in which the method and the device according to theinvention have been applied.

FIG. 2 illustrates a fuel injection system in accordance with theinvention, intended primarily for a four-stroke engine.

FIG. 3a illustrates schematically a carburettor intended to beincorporated in a fuel supply system in accordance with the invention.

FIG. 3b is in a part enlargement of an area illustrated in FIG. 3a bymeans of dash- and dot lines.

FIG. 3c illustrates an alternative embodiment of the part solution ofFIG. 3b, illustrated by means of a circle delimited by a dash- and -dotline.

FIG. 4 illustrates, by means of the upper row of curves the operativepressures, i.e. the fuel drawing pressures and the positions of to theshut-off valve. The row below illustrates two curves representative ofthe resulting fuel flow, one with respect to the flow when a shut-offvalve is not in operation and the other one when a shut-off valve is inoperation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the schematically illustrated drawing FIG. 1 numeral reference 1designates an internal combustion engine of a two-stroke type. It iscrank case scavenged, i.e. a mixture 40 of air 3 and fuel 4 from acarburettor 9 or a low pressure fuel injection system 10 is drawn to theengine crank house. From the crank house, the mixture is carried throughone or several scavenging passages 14 up to the engine combustionchamber 41. The chamber is provided with a spark plug igniting thecompressed air-fuel mixture. Exhausts 42 exit through the exhaust port43 and through a silencer 13. All these features are entirelyconventional in an internal combustion engine and for this reason willnot be described herein in any closer detail. The engine has a piston 6which by means of a connecting rod 11 is attached to a crank portion 12equipped with a counter weight. In this manner the crank shaft is turnedaround. In FIG. 1 a piston 6 assumes an intermediate position whereinflow is possible both through the intake port 44, the exhaust port 43and through the scavenging passage 14. The mouth of the intake passage 2into the cylinder 5 is called intake port 44. Thus the intake passage isclosed by the piston 6. By opening and closing the intake passage 2varying flow speeds and pressures are created inside the passage. Thesevariations largely affect the amount of fuel 4 supplied when the fuelsupply system 8 is of carburettor type 9 or is a low-pressure injectionsystem 10. Such a fuel injection system normally operates at a pressureof two to three bars and said pressure variations then give rise to aconsiderable change of the amount of fuel. A carburettor has aninsignificant fuel feed pressure. The amount of its fuel feed isentirely affected by pressure changes in the intake passage 2.High-pressure injection systems, on the other hand, may operate atpressures of 100 bars and in that case the effects are almostnegligable. The subject invention makes use of these fuel amountvariations in order to create simple and safe control of the amount offuel supplied and it is therefore directed primarily to the fuel supplysystem the supplied amounts of which are essentially affected by thevarying flow speeds and pressures inside the intake passage that arecaused by the opening and the closing of the latter.

FIG. 2 illustrates a fuel supply system 8 which is of a low pressureinjection system type 10 or of carburettor type 9. In the latter casethe carburettor 9 is located upstream of the fuel supply line 19. Thedrawing figure is a cross-sectional view through the cylinder head of aninternal combustion engine. The cylinder head delimits the combustionchamber 5 of the engine in a direction downwards. The cross-sectionalview is taken in such a manner that the intake passage and the value 7that opens and closes the passage 2 are clearly indicated. The enginemay be of a four-stroke or a two-stroke type, usually however it is of afour-stroke type. The opening and closing movements of the valve 7 arecontrolled by a cam shaft having a protrusion 15 affecting the valvestem. This solution is entirely conventional and for this reason willnot be dealt with any further herein. On the other hand, an additionalprotrusion 18 is formed on the cam shaft, affecting a metering needle 17in the fuel supply system 8. In this manner the metering needle 17 isopened and closed upon each turn of the cam shaft. In other words, themetering needle 17 acts as a shut-off valve cutting off fuel supply tothe intake passage 2. Fuel is carried through a first fuel line 19 up tothe metering needle 17 and from the latter through the fuel line 20debouching into a venturi 45. The latter is a narrow part of the intakepassage 2. Owing to the narrow configuration the flow speed of the air 3is increased and thus a suction force is generated at the mouth of thefuel line 20. Owing to the supply pressure of the fuel 4 and thissuction force, fuel is supplied to the intake passage 2. Because thevalve 7 is opened and closed varying flow speeds and pressures arecreated inside the intake passage, like in the case of thepiston-operated intake passage 2 in FIG. 1. Obviously the relativevalues of the depression in the venturi area drawing fuel and the supplypressure 4 may be varied considerably within the scope of the invention.For instance, in case of a total absence of a venturi arrangement incombination with a simultaneous low supply pressure with respect to thefuel 4, the fuel-supply amounts in the intake passage 2 would still besubstantially affected by closure and opening of the valve 7. Normally,depression variations amount to some or some tenths of a bar and thesupply pressure perhaps to 2 to 3 bars in the case of a low pressuresystem. It could also be noted that the cut-off could also related to apart flow of fuel 4. In this case there is parallel injection of fueland this is not affected by a valve 7. Cut-off of fuel supply 4 to theintake passage 2 is affected during a part of one revolution of theengine and essentially takes place during a part of the enginerevolution during which the intake passage is closed and consequentlythe feed of fuel is reduced or has ceased. In this manner simple andefficient fuel amount control is obtained as will be explained in moredetail in connection with drawing FIG. 4.

FIG. 3a illustrates a carburettor to be used with the fuel supply systemin accordance with the invention. Supply of fuel 4 is effected to fuelnippel 21 on a carburettor 9. From this nippel fuel is carried to a fuelstorage 22 which is delimited downwards by a membrane 23. So far thecarburettor is a conventional membrane carburettor and therefore neednot be commented upon further. Also other types of carburettors that arearranged to supply fuel in a similar manner for further treatment arepossible.

FIG. 3b illustrates on an enlarged scale the manner in which thisfurther treatment after the fuel storage 22 is effected. From thestorage 22 a line leads to a cut-off valve 24. The latter is in the formof a solenoid or electromagnet. Upon energization, a closure plunger 29is forced forwards, closing off the interconnection between the storage22 and the fuel lines 26', 26, 25 leading to the venturi in thecarburettor. A compression spring 34 ensures that the closure plunger ispulled back and opens up the passage as soon as the energization ceases.The closure plunger 29 is attached to a piston rod travelling in a guide30 and at the opposite face of the piston rod is arranged e.g. an ironcore which is attracted by an energized coil so as to be moved outwards.In other words, the solenoid is of a normally open type. However, itgoes without saying that it could also be of a normally closed type. Inthe latter case the closure plunger 29 opens up the fuel passage as thesolenoid is energized. Decisive in this choice are features such ascurrent consumption, functional reliability and so on. By choosing anormally open type it is precisely the functional reliability that isincreased. For, should the energization fail, the basic function of thefuel supply system still remains. Only the finer adjustment of the fuelsupply amount ceases. Down-stream of the closure plunger 29 a shortpassage 26' leads to a branch of a wider channel 26 and smaller channel25. The smaller channel 25 leads to the venturi and is used as a socalled idling nozzle whereas the coarser channel 26 also leads to theventuri and is used as the principal nozzle. This is in analogy withconventional carburettor technology. However, the design may lead to acertain disadvantage in cases when an increase of the rotational speedtakes place from an idling situation. For in such cases, fuel might bedrawn back from the channel 25 and into the channel 26, whereby asurplus amount of fuel is supplied through the principal nozzle. Thismeans that also after the closure plunger 29 having cut-off the supplyfrom the storage 22 the fuel amount is available both in channel 25 andchannel 26 to be sucked through both nozzles. Normally, this is effectedthrough the principal nozzle. This effect may, however, be avoided withthe aid of the solution according to FIG. 3c, which is an enlargement ofthe encircled area in FIG. 3b. In this case the short fuel line 26' isomitted. Instead, both channel 25 and channel 26 debouch into the cavityin which the closure plunger 29 operates. When in this case the closureplunger is moved forwards for closing purposes both channel 25 and 26are closed and therefore no fuel from channel 25 can be sucked outthrough the channel 26 up to the principal nozzle. Also in the case ofcarburettors it may be appropriate to close off only a part flow withthe aid of the shut-off valve 24. This solution could be of interestwhen the invention is used in four-stroke engines and the intake passage2 leads directly into the engine combustion chamber. In this case thereis no buffer capacity in the crank case and the change with respect tothe brief cut-off of the fuel flow will become much more abrupt.

As mentioned above the invention aims at providing for improvements inseveral respects. This will become most clearly apparent through anexamination of the graphs in FIG. 4 in which the various curvesillustrate the effects on fuel flow from the actuation of the closurevalve in various cases in a two-stroke engine. The upper part of thedrawing figure illustrates curves P relating to an operative depressionsituation, i.e. the pressure drawing fuel into the intake passage 2.This depression P is a combination of the static and the dynamicpressures. The horizontal axis illustrates the crank angle positionexpressed as engine revolutions. Along the axis the positions withrespect to opening O and closing S of the intake passage 2, respectivelyare marked. Opening and closure are effected either with the aid of thepiston 6 or with the aid of a special valve 7. It should be observedthat the axis representative of the engine revs is broken immediatelyfollowing one engine revolution. To the left of the break is shown onefuel flow control variety and to the right another one. In conjunctionwith the upper pressure curve P is also illustrated a curve of squareconfiguration, illustrating the manner in which the brief closure offuel supply is effected. The examples of FIG. 4 are representative ofthe case in which the fuel supply is cut off completely since this isthe situation most easy to discuss. But also the complete closure of apart flow could be intended, like previously. In positions A, D at thebottom of the engine revolution axis the fuel supply is fully open, i.e.the cut-off valve 24; 17 is open. At points B, C and therebetween is, onthe other hand the valve is fully closed. The distance A-B illustratesthe manner in which the valve moves from open to closed and C-D fromclosed to open. This concerns the variety of control to the left of thebreak in the curve. In accordance with the variety to the right of thebreak the square curve has been moved back in relation to the P-curveand it has also been partly prolonged. Opening and closing of the fuelsupply is effected in analogy therewith according to E-F-G-H. A furthercondition with respect to the curves in FIG. 4 is that the fuel feed isaffected solely on account on the effective depression P. This is atypical case in most carburettor applications. Quite simply, these areconstructed in such a manner that the amount of passing air is todetermine the fuel amount. In a low pressure injection system 10 theconditions are somewhat different but also in that case the suppliedfuel amount is affected to an essential degree by changes in theoperative pressure. Accordingly, the same control principles apply as inthe case of a carburettor. Closure curves A-B-C-D and E-F-G-H in realityhave somewhat rounded "corners" B, C, F, and G.

The left hand side of the diagram illustrates how the operativedepression P increases from zero at point O, where the intake passage 2is opened, to a maximum point then again back to zero at point S wherethe intake passage 2 is being closed. After closure, the depressionsinks on the negative side. This means that a slight over-pressureresides in the intake passage at the position of fuel injection. Thepressure then oscillates back in such a manner that thereafter adepression pulse is generated and another over-pressure pulse, followedby a slight depression pulse. This is of course only a pedagogicalexample but must be regarded as rather normal situation in the process.Thus, closure of the intake passage 2 results in a process ofoscillation of the operative pressure. Straight below the curverepresentative of the operative pressure is shown a curve that isrepresentative of the resulting fuel flow in two cases. The dotted lineillustrates the case F1 when there is no cut-off of the fuel supply,i.e. no closure function according to curves A-B-C-D or E-F-G-H. In thiscase it is assumed that the resulting fuel flow is directly proportionalto the operative pressure, which is a common situation. This means thatthe dash- and dot curve F1 is exactly similar to curve P up to point S.Since an over-pressure in the fuel nozzle cannot produce supply of fuelback into the carburettor nozzle no negative fuel flow may exist, i.e.fuel flow becomes zero when the P-curve is negative. On the other hand,as soon as curve P becomes positive, fuel delivery is effected. Thisresults in the two "peaks" 34, 35. In the diagram this fuel flow curvethus is designated by F1.

When on the other hand cut-off of the fuel flow according to A-B-C-D orE-F-G-H occurs, the fuel flow is changed. This is illustrated by thecontinuous-line curve F2. From point O further to the left these curvesare identical up to point A'. For in point A in the upper diagram theshut-off valve begins to close, which results in throttling of the fuelflow, resulting in curve F2 having a different progress from curve F1.In point B complete cut-off of the fuel flow is achieved and thiscorresponds to point B' in the lower diagram. At point B' fuel flow thusis zero. By cutting off the fuel flow according to curve A-B-C-D fuelflow thus has been reduced correspondingly, primarily by area 33 in thedrawing figure. But also the "peaks" 34 and 35 have disappeared. This isdue to the fact that the fuel supply is completely cut off duringprogress B-C. Fuel amounts corresponding to areas 33, 34 and 35consequently have disappeared owing to the fuel cut-off according toA-B-C-D. This corresponds to the left-hand control variety in thedrawing figure and the same applies to the right hand side. Two aspectsare of interest. In the first place the "peaks" 34 and 35 disappear.This is positive since the "peaks" 34 and 35 are caused solely by apressure oscillation in the intake passage 2. When the passage is closedthere is no real air flow therein that could motivate a correspondingfuel flow. Conventional carburettors are calibrated so as to considerthe "peaks" 34 and 35 as far as possible. Obviously, the number of"peaks" could be both larger than two or less than two. However, suchcalibration is difficult and uncertain, since the oscillation phenomonis affected by several factors and changes with the rotational speed.The removal of this "peaks" thus has resulted in more accurate fuelsupply. At the same time it is also desirable to add fuel to an airflow, allowing the fuel drops to be carried straight into the engine.For several reasons it is thus desirable to remove these two "peaks" 34and 35.

The cut-off curve representative of fuel flow shows a dotted line a-bwhich is essentially parallel to A-B. By instead using cut-off curvea-b-C-D the size of area 33 could be reduced. Point a, representative ofthe instance when the cut-off valve begins closing, in this case insteadcorresponds to point a' and in the example shown the area 33 is reducedapproximately by half. This means that a larger amount of fuel is addedin this case. Precisely by varying the position of the front flank A-Bit becomes possible to control the amount of fuel supply. Cut-off of theentire fuel flow or of a part flow is arranged to occur essentiallyduring a part of an engine revolution when the intake passage is closed,i.e. between points S-O in the diagram. Fuel amount control thus iseffected by varying one flank in the cut-off curve. In the first case itis flank A-B, i.e. the front flank, that is varied. In the second case,shown to the right of the break, it is instead the rear flank G-H thatis varied. In both cases the cut off curve is arranged in such a waythat it affects only one side of each fuel supply progress from point Oto point S, i.e. opening and closure of the intake passage 2. This is anadvantageous accuracy feature, since any tolerance displacement of thecut-off curve in any direction then will only affect one of the twoneighbouring fuel supply progresses. Obviously the principle may also beapplied in such a way that this influence occurs on both sides of eachfuel supply progress between points O and S. The first case of controlto the left thus is characterized by the fact that a brief cut-off ofthe entire fuel flow or of a part flow is started before the intakepassage 2 is closed by the piston 6 or the valve 7, i.e. in point S. Thecut-off has essentially ceased before opening of the intake passage 2 isagain started by the piston or by the valve 7, i.e. in point O. Inaccordance with the other control variety to the right of the break thecut-off begins only after closure of the intake passage 2 by the piston6 or the valve 7, i.e. in point S. The cut-off ceases entirely onlyafter opening of the intake passage having again begun by means of thepiston 6 or the valve 7. i.e. in point O.

The basic feature of this control principle thus is that a comparativelylong cut-off in time is made and this cut-off is arranged to essentiallytake place during a portion of one engine revolution, or more preciselyworking cycle, when the intake passage is closed and consequently thefuel supply is reduced or has ceased. This means that the amount of fuelsupplied can be precision-adjusted by a slight displacement of one ofthe flanks of the shut-off valve cut-off curve. A common feature of eachone of the control situations is that a change of the state of theshut-off valve 24; 17, i.e. from closed to open or alternatively fromopen to closed, is arranged to essentially take place within thecylinder suction phase, i.e. between O and S, whereas changes of stateassociated with this change, i.e. immediately preceding or immediatelyfollowing changes of the state of the shut-off valve 24; 17, i.e. fromopen to closed or alternatively from closed to open, essentially takeplace outside the cylinder drawing phase, so that fuel supply regulationtakes place essentially in conjunction with one of the changes of stateof said shut-off valve 24; 17. As already mentioned, this is anadvantage from an accuracy point of view. Had on the contrary a briefcut-off been made entirely during an ongoing fuel supply it would havebeen necessary to re-open the valve very rapidly in order to avoid a toolarge reduction of the fuel. However, such rapid precision control ofvalves is very difficult to perform. The method in accordance with theinvention on the other hand makes it possible to considerably increasethe length of the cut-offs of the fuel supply, which is veryadvantageous from a regulating point of view. Shut-off valves of thison-off type are very simple and functionally reliable and therefore itis an advantage to make use of this type of valve instead of varyablethrottling. From a control point of view it is thus very advantageous tobe able to affect the length of the cut-off progress, provided that thislength is of reasonable extent. By arranging, in this case, for thecut-off to take place essentially during that portion of the enginerevolution during which the intake passage is closed such reasonableextent of the cut-off progress is achieved. It is likewise possible toopen a normally closed valve. In both types of valves it is essential toincrease the period between changes of state with respect to the cut-offvalve. This is achieved by arranging for the states of change to takeplace essentially within and outside, respectively, the suction phase asindicated above. The examples of control given in FIG. 4 relate to atwo-stroke engine. The only difference therefrom with respect to afour-stroke engine is that the fuel supplies and consequently valveclosures will occur half as often on account of the basic constructionof the engine. In accordance with the examples given, the control of thefuel amounts have been performed at each possible occasion, i.e. inconnection with each instance of fuel supply between O and S. However,this is not necessary. Instead it may in many cases be an advatange toperform adjustments more rarely. This is true particularly in crank casescavenged two-stroke engines or crank case scavenged four-strokeengines. In such cases the crank case can hold a considerable amount offuel and consequently serves as a nivelling reservoir. In this manner itbecomes possible to perform major fuel amount adjustments in two-strokeengines upon every other, every third or possibly every fourth enginerevolution instead of upon each engine revolution and, in the case of afour-stroke engine, half as often. In other words the cut-off is noteffected at each possible occasion but instead at every other or everythird or possibly every fourth possible occasion. Possible occasion thuswould be in connection with each fuel supply when the intake passagesopen, i.e. between O and S.

The opening and closing movements of the shut-off valve 24; 17 thus iscontrolled by the engine revolution position. This is effected in amechanical-hydraulical or mechanical-pneumatical way. FIG. 2 illustratesa mechanical solution wherein the metering needle or the shut-off valve17 closes off the entire fuel flow or a part flow on each possibleoccasion. FIGS. 3a and 3b illustrate the solution according to which thecontrol is effected electrically. The shut-off valve 24 could becontrolled for instance by a control computer so that cut-offs will takeplace to an essential extent during a part of the engine revolution whenthe intake passage is closed. In addition, it is quite simple to varythis control in such a manner that it does not take place on everypossible occasion but instead on perhaps every other, every third orpossibly every fourth possible occasion. In that case a major fuelamount adjustment is made instead. In consequence thereof it is nolonger needed to activate the shut-off valve 24 as often, which leads toa considerable reduction of energy consumption, which is of greatimportance in many applications. In this case the control computercommands closure of valve 24 only on every other or every third orpossibly every fourth possible occasion.

I claim:
 1. A method of controlling the amount of fuel delivered to acombustion engine (1), wherein the fuel is supplied through an intakepassage (2) intended to deliver air (3) and fuel (4) to one cylinder(5), said intake passage being opened and closed by a piston (6) andwherein the fuel supply to the intake passage (2) is effected upstreamfrom the piston (6) and wherein, in response to the opening and closingof the intake passage (2), varying flow speeds and pressures areproduced in the intake passage, the fuel supply system (8) beingsubstantially affected by this variation and, in order to regulate thefuel supply to the engine, a cut-off takes place in the fuel-supplysystem (8) during a portion of the operating cycle by a shut-off valve(24; 17) which shuts off at least a part of the fuel flow, wherein achange of the state of the shut-off valve (24; 17) is arranged to takeplace during the cylinder suction phase, whereas a change of stateassociated with this change, essentially takes place outside thecylinder suction phase, so that fuel supply regulation takes placeessentially in conjunction with one of the changes of state of saidshut-off valve (24; 17).
 2. A method as claimed in claim 1, wherein theshut-off valve (24; 17) is operable to shut off the entire fuel flowduring a portion of the operating cycle to regulate the fuel supply tothe engine.
 3. A method as claimed in claim 1, wherein the fuel supplysystem (8) is a carburetor type (9) system.
 4. A method as claimed inclaim 1, wherein the cut-off is arranged to prevent fuel supply (34, 35)to the intake passage (2) caused by oscillation phenomena arising inconnection with the closure of the intake passage by the piston.
 5. Amethod according to claim 1, wherein the cut-off is arranged to startbefore the piston (6) has closed the intake passage (2), and is arrangedto cease essentially before the piston (6) again begins to open theintake passage (2).
 6. A method as claimed in claim 1, wherein thecut-off begins only after closure of the intake passage (2) by thepiston (6), and wherein the cut-off ends only after the intake passagehas again been opened by the piston (6).
 7. A method as claimed in claim1, wherein the cut-off is effected only on non-consecutive occasions. 8.A method as claimed in claim 1, wherein the shut-off valve (24) isoperated electrically, and is of a normally open type, and whereincut-off is effected by supply of current to the valve.
 9. A device tocontrol the amount of fuel supplied to an engine (1), wherein the fuelis delivered through an intake passage (2) intended to deliver air (3)and fuel (4) to one cylinder (5), said intake passage being opened andclosed by a piston (6) and wherein the fuel supply to the intake passage(2) is effected upstream from the piston (6) and wherein, in response toopening and closing of the intake passage (2), varying flow speeds andpressures are produced in the intake passage, the fuel supply system (8)being operable to supply different amounts of fuel in response to theflow speeds and pressures in said intake passage and includes a shut-offvalve (24; 17) which at least partially cuts off the fuel supply flowduring a portion of the operating cycle, and a change of the state ofthe shut-off valve (24; 17) takes place during the cylinder suctionphase whereas a change of state associated with this change essentiallytakes place outside the cylinder suction phase, so that fuel supplyregulation takes place in conjunction with one of the changes of stateof said shut-off valve (24; 17), and means for opening and closing theshut-off valve in response to the engine revolution position.
 10. Adevice as claimed in claim 9, wherein the shut-off valve (24) iselectrically controlled and is a normally open type of valve.
 11. Adevice as claimed in claim 9, wherein the shut-off valve (24) iselectrically controlled and closing of the shut-off valve is commandedonly on non-consecutive occasions.
 12. A device as claimed in claim 9,wherein the fuel supply system (8) is a carburetor (9) comprising atleast one fuel supply line (25) leading to a low-speed nozzle and atleast one fuel supply line (26) leading to a high-speed nozzle, saidlines merge in a common line (26) and the shut-off valve (24) isarranged to shut off said common line (26).
 13. A device as claimed inclaim 9, wherein the fuel supply system (8) is a carburetor (9)comprising at least one fuel supply line (25) leading to a low-speednozzle and at least one fuel supply line (26) leading to a high-speednozzle, the shut-off valve is arranged to shut off both lines (25, 26)simultaneously.